48GA004 datasheet(102/268 Pages) MICROCHIP

102 / 268 page

PIC24FJ64GA004 FAMILY

DS39881D-page 102

 2010 Microchip Technology Inc.

8.4.3

SECONDARY OSCILLATOR

LOW-POWER OPERATION

The Secondary Oscillator (SOSC) can operate in two

distinct levels of power consumption based on device

configuration. In Low-Power mode, the oscillator

operates in a low-gain, low-power state. By default, the

oscillator uses a higher gain setting, and therefore,

requires more power. The Secondary Oscillator Mode

Selection

bits,

SOSCSEL<1:0>

(CW2<12:11>),

determine the oscillator’s power mode.

When Low-Power mode is used, care must be taken in

the design and layout of the SOSC circuit to ensure that

the oscillator will start up and oscillate properly. The

lower gain of this mode makes the SOSC more

sensitive to noise and requires a longer start-up time.

8.4.4

OSCILLATOR LAYOUT

On low pin count devices, such as those in the

PIC24FJ64GA004 family, due to pinout limitations, the

SOSC is more susceptible to noise than other PIC24F

devices. Unless proper care is taken in the design and

layout of the SOSC circuit, it is possible for

inaccuracies to be introduced into the oscillator's

period.

In general, the crystal circuit connections should be as

short as possible. It is also good practice to surround

the crystal circuit with a ground loop or ground plane.

For more detailed information on crystal circuit design,

please refer to the “PIC24F Family Reference Manual”,

Section 6. “Oscillator”

(DS39700) and Microchip

Application Notes: AN826, “Crystal Oscillator Basics

and Crystal Selection for rfPIC® and PICmicro®

Devices” (

DS00826) and AN849, “Basic PICmicro®

Oscillator Design”

(DS00849).

Note:

This feature is implemented only on

PIC24FJ64GA004 family devices with a

major silicon revision level of B or later

(DEVREV register value is 3042h or

greater).

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